Vehicle operation requires the ability to see. Historically, this has meant that a human driver must be able to see around a vehicle they are operating to safely operate the vehicle. However, as automobiles, heavy trucks, and other vehicles have evolved over time, so too have the systems and components that enable the driver's ability to perceive the vehicle's surroundings. Examples include the invention of windshields, windshield wipers, wiper fluid, headlights, high beams, tail signals, stop signals, turn signals, marker lights, rear and side view mirrors, window defogging systems, window tinting, window shades, etc. More recently, examples include sensors like backup cameras, radar, and other advanced driver assistance systems (ADAS), which further include LIDAR, FLIR night vision, sonar, etc. It is expected that vehicles will increasingly rely on an array of perception sensors like cameras and LIDAR to “see” and navigate. Accordingly, it is expected that the safe and effective operation of vehicles will increasingly depend upon reliable functioning of such perception systems.
A vehicle's perception surfaces (e.g., windshield, mirrors, headlamps, sensors, etc.) are affected by the environment in which the vehicle operates. Common environmental obstructions include snow, ice, mud, insect splatter, and bird droppings. A vehicle can be expected to experience a variety of these situations in any given trip, leading to frequent and fast-developing changes in its ability to “see,” as well as the driver's ability to see. Further, vehicles are often stored outside in ever-changing environmental situations. A common occurrence is windshield frost, which can be difficult to manually remove, and which today's vehicle systems often struggle to remove in less than ten minutes. This results in vehicles being left to cold idle, which consumes fuel, results in unnecessary vehicle emissions, and wastes drivers' time. Moreover, some drivers may start driving prematurely—before having clear and safe vision—increasing the likelihood of accidents.
Current vehicle designs may include several systems for removing obstructions from perception surfaces, such as electric heaters, warm air flow, specialized coatings, mechanical wipers, wiper fluid, vibrating surfaces, and spinning surfaces. Electric heaters, for example, often consist of thin wires embedded in surfaces to be cleared of ice (e.g., a windshield) or in materials put in contact with the surfaces, and can still require ten or more minutes to effectively clear a surface. Moreover, such heaters provide heat for deicing—but do not dissolve, mechanically remove, or mobilize other obstructions away from the surface. In some instances, such systems can add significantly to the cost of a vehicle, particularly for surfaces, such as a windshield, that may be damaged or replaced during a vehicle's lifetime.
Oppositely, wipers and fluid can dissolve, mobilize, and mechanically remove some obstructions. However, they are inadequate for many types of obstructions, and they do not provide thermal energy to hasten removal of ice, snow, bug splatter, etc. Further, washer fluid is commonly composed of water and up to 50% alcohol (methanol or ethanol) to ensure that wiper fluid does not freeze or “refreeze” after application (e.g., spraying)—which can reduce visibility and/or damage the vehicle as the frozen fluid expands. An unfortunate side effect of using alcohol is the strongly inverted correlation between temperature and fluid viscosity. Cold alcohol-water mixtures have been shown to have viscosity five (or more) times higher than warm fluid, resulting in situations where warm fluid sprays evenly across the windshield, but cold fluid trickles out and only reaches a short distance from the spray nozzles at greatly reduced flow rates. Therefore, it is highly desirable to heat washer fluid before pumping it onto perception surfaces of a vehicle.
One challenge with the use of washer fluid in surface cleaning is that washer fluid is consumed in the process. Bottled washer fluid (or additive concentrate added to water) can be expensive, requires effort to replace, and washer fluid reservoirs take space and add significant weight to a vehicle. Vehicle engineers place a high premium on the weight and volume of vehicular systems, especially when a vehicle's design borders on a weight class limit. Systems that do not efficiently use washer fluid will result in inconvenience and cost to the vehicle owner and may not be readily implemented in automotive designs by engineers. Therefore, it is highly desirable to utilize as little washer fluid as possible in cleaning perception surfaces.
Moreover, washer fluid premixes can pollute the air, ground, and water, which is becoming more problematic as the number of vehicles in the world increases (presently there are over 1 billion vehicles and growing). For example, the European Union (EU) has passed strict restrictions on the amount of antifreeze that may be in washer fluid. Therefore, vehicles in the EU commonly have warming coils, electrically heated washer hoses, and/or electrically heated nozzles to thaw and maintain washer fluid above freezing. An associated problem with efficiently providing heated fluid to perception surfaces without wasting fluid is that any tubing carrying heated washer fluid from the heating source to the point of application loses heat to the surrounding environment. Even when fluid in this tubing is very hot, it quickly cools and approaches ambient temperature. To subsequently deliver hot fluid through the tubing, the previously cooled fluid must first be removed from the tubing (e.g., via spraying) prior to the arrival and delivery of hot fluid. Accordingly, more effective means to economize on washer fluid usage and improve the efficiency of its use have become a significant need for the future—especially where autonomous or other vehicles may include many vehicle components (e.g., 30 or more per vehicle) that require periodic cleaning.
Additionally, perception devices, such as high-resolution electronic cameras, LIDAR systems, LED lighting system, etc., generate heat that can increase the operating temperatures of these devices above their indicated operating ranges. Moreover, when temperatures rise, the lifetime and performance of such devices decrease. Similarly, other devices within a vehicle—such as those containing batteries—must be maintained within certain temperature ranges and can therefore benefit from heating. These temperature constraints often present challenges with locating and mounting the devices on a vehicle, and with the design and packaging of the devices themselves. For example, devices that tend to overheat typically require larger surface areas or even supplemental cooling fins, such as those found on the back of LED headlights.